CEBPB mRNA and protein levels in STI571-treated 32D-BCR/ABL cells. (A) Northern blot analysis on total (lanes 1 and 2) or polysome-associated (lanes 3-4) RNA from untreated (lanes 1 and 3) or STI571-treated (2 μM, 12 hours) 32D BCR/ABL cells (lanes 2 and 4). A 500-base segment of the c/ebpβ mRNA 3′UTR was ³²P-radiolabeled and used as probe; 28S and 18S are shown as a control of equal RNA loading. (B) Western blot analysis of CEBPB expression in total extracts from 32Dcl3 cells, untreated and STI571-treated (1 μM, 24 hours), 32D-BCR/ABL cells, untreated and STI571-treated (2 μM, 24 hours) mononuclear cells from a CML-BC sample. Western blotting with an anti-GRB2 antibody was used as control of equal loading. (C) Western blot shows CEBPB and tyrosine-phosphorylated BCR/ABL levels in 32Dcl3 cells transduced with MigRI-BCR/ABL and sorted by low and high GFP expression. Anti-GRB2 Western blotting was used as control of equal loading. (D) Histogram (top) and Western blot (bottom, first row) show CEBPB protein levels (expressed as mean ± SE of densitometric units after normalization with GRB2 levels) in the CD34⁺ fraction from bone marrow of healthy donors (NBM; n = 3), CML-CP (n = 3), and CML-BC (n = 3) patients (NBM versus CML-CP, *P = .137; CML-CP versus CML-BC, **P < .001; t test). The Western blot in the second row shows CEBPB levels in 2 of the 3 NBM, CML-CP, and CML-BC samples still available for a second analysis.